Use In Meshed Networks; Daisy Chain - GE F650 User Manual

APPENDIX B: B.2 RSTP (IEEE 802.1D-2004) AND DAISY CHAIN
B.2.3 Use in meshed networks
One great strength of RSTP is its support for all kinds of meshed topologies. The resulting flexibility regarding the
installation is a clear advantage over the stringent restrictions that are imposed by ring protocols such as MRP and ring
installations. However, this flexibility harbors one great disadvantage, namely the reconfiguration time, which for an
interconnected network depends – among other things – on the complexity of the network topology and the location in
the network at which the failure occurred. Since RSTP is a decentralized protocol, it may also provoke highly unpredictable
race conditions in the establishment of new communications paths, particularly when choosing a new root bridge. This
gives rise to network reconfiguration times that can be estimated only very roughly, and this does restrict the use of RSTP,
particularly in meshed networks. In the case of meshed networks with very little complexity (such as ring networks with
two or three additional loops or subrings), a detailed analysis can make it possible to determine upper limits, but these
always need to be worked out individually. Unlike with the protocols MRP, HSR and PRP, it is not possible to make a general
statement.
B.2.4 Daisy chain
A daisy chain is an interconnection of devices where each device is connected in series to the next.
With an Ethernet daisy-chain redundancy selected, the F650 has two Ethernet ports and it is working as an Ethernet
unmanaged switch. The two Ethernet ports are used for connecting each device to the ports of its two neighboring
devices.
Each device in the daisy chain forwards the message until it reaches the destination.
Ports A and B use the same MAC (physical device) address and operate by chaining one device with the next one.
Note that it is important not to create a loop in this topology. Both ends of the chain can be connected to different
networks. The device operates only with one IP address through these 2 ports.
GEK-113000-AF F650 DIGITAL BAY CONTROLLER b-7